If the link doesn't work search the Getaway forum for "hobie safety lessons learned". I think the consensus is that a tether is a bad idea, and that an overturned Getaway moves faster than you can. You and the crew need to hold on when you go over. If you have the tiller and main sheet in hand, you are unlikely to fall off while sailing and should be able to hold on in a capsize. Warn your new crew member that if you do capsize and they get seperated from the boat not to panic and enjoy the swim until you can get back to them.
Registration decals stick just fine. The problem is removing them.
I suggest you upgrade right from the start to a Harken mainsheet block. It is much easier for a new cat sailor to cleat and uncleat. Failure to let the main sheet out in a puff, is one of the most likely ways for a new cat sailor to get to go for an unplanned swim.